There is known a ring transformer for resistance butt welders, comprising a closed magnetic core of a shape that essentially corresponds to that of articles being welded, as well as a primary winding and a secondary winding arranged on the magnetic core and uniformly extending along the butts of articles to be welded (cf. USSR Inventor's Certificate No 93,847, Cl. 21 h 32/03, published in 1964).
The magnetic core of the transformer under review is a solid member of a round, rectangular or polygonal section. If necessary, the core may be split in the longitudinal direction and provided with an appropriate joint. Thus the shape of the magnetic core is invariably designed for a specific article, wherefore the welder incorporating such a transformer cannot be used for welding articles of different cross-sectional configurations.
The primary winding must be drawn through a hole of a non-detachable closed magnetic core; this is an arduous manual operation which hardly lends itself to mechanization. If the magnetic core is detachable the individual sections of the primary winding are fitted over it from its ends so that there is a wide gap between the core and the winding, which accounts for increased losses and a reduced efficiency and thus affects the transformer's parameters. Another disadvantage is the presence of an open area on the lateral surfaces of the primary and secondary windings, which is hard to insulate. As a result, the primary winding may be shorted against the secondary winding or the magnetic core by drippings liberally produced in the course of butt welding. A breakdown of a portion of the primary or secondary windings makes it necessary to dismount and rewind the transformer, which often involves a dismantling of the whole welder.